The present invention relates to flow control valves and, more particularly, to a pressure operated drain valve for draining water in a vehicle sanitation system.
In most vacuum flush aircraft toilet systems, flushing water is supplied to the toilet bowl by a water supply line connected between the bowl and a water tank containing the aircraft's potable water supply. However, using the potable water supply of the aircraft to flush toilets is not an efficient use of the water. Under present airline standards, approximately eight ounces of water is removed from the potable water supply for each bowl flushing operation. Since aircraft toilets are flushed dozens and dozens of times each flight, the use of potable water is significant and adds excess and unwanted weight to the aircraft. It also limits the use of potable water for other necessary functions in the aircraft and increases fuel consumption.
In order to minimize the use of potable water to flush the toilet bowl, it was discovered that used wash water from the lavatory sinks could be collected and reused for flushing purposes. As a result, a need has arisen for a system to reuse this wash water, commonly referred to as "grey water", for flushing toilet bowls. In the process of reusing the sink wash water it is important that the grey water never enter and thereby contaminate the supply lines containing potable water. Accordingly, appropriate precautions must be taken to ensure that the grey water is always kept separate from the potable water.
In designing a sanitation system that uses grey water, it is desirable to incorporate some type of drain valve for draining the grey water from the lines. In general, the grey water drain valve must be closed when the water supply lines of the aircraft sanitation system have been pressurized, to thereby allow the system to function properly when in use. The drain valve also must be capable of draining the grey water in the lines when the water supply lines are depressurized and the system is not in use. Draining all of the water in the lines is of special concern in situations where the aircraft will not be used and is stored in an environment subject to freezing temperatures. In these situations, the water supply lines in the aircraft will not be pressurized and it is necessary to drain all water from the supply lines. If the lines are not properly drained, freezing temperatures within the aircraft cabin during parking or storage of the aircraft can cause any water remaining in the lines to freeze, and thereby expand and possibly burst the lines. At best, the frozen water may be difficult to thaw and, therefore, may unduly delay or prevent operation of the sanitation system upon reactivating the aircraft. Since the grey water used to flush the toilet bowl ultimately comes from the potable water supply tank, antifreeze additives or the like cannot be put into the water to prevent freezing without contaminating the water and preventing its other necessary uses within the aircraft.
Accordingly, there has existed a definite need for a drain valve which closes when the water supply lines are pressurized to allow grey water to be used for flushing purposes, and which will conveniently drain the grey water in the line when the system is not pressurized. There also has existed a need for a drain valve that maintains the potable water and grey water separate from each other at all times. The present invention satisfies these needs and provides further related advantages.